Multiple layer foam insert for tires

ABSTRACT

A multi-layer or multi-element foam insert for a pneumatic inner tube emulating the effect of air pressure, across a wide range of temperatures and pressures, while maintaining the weight of a conventional air-tilled pneumatic tube. By combining materials of different density and/or the orientation and thickness of such materials, favorable handling properties are achieved.

CROSS REFERENCE TO RELATED INVENTION

This application is a continuation (or divisional) of Non-Provisional Utility U.S. patent application Ser. No. 15/292,664 entitled “Multiple Layer Foam Insert for Tires” and claims the benefit of, and priority to, Provisional Application No. 62/391,063, filed on Apr. 19, 2016, entitled “Round Tubular Structure Comprised of Multi Density Extruded Foam . . . [to] Allow the characteristics of Pressure, Performance and Weight to be Manipulated to Achieve any Desired Performance”. The benefit under 35 USC § 119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.

BACKGROUND Field of the Invention

The invention pertains to the field of inner tubes for vehicle tires. More particularly, the invention pertains to a foam insert for use in tire and tube systems in bicycles, motorcycles, automobiles, trucks and other vehicles.

Description of Related Art

The susceptibility of the pneumatic tire to puncture is inherent in the nature of the elastomeric material that comprises the tire or the tire and the inner tube in the case of a bicycle or tube-type motor vehicle tire. When inflated, such elastomeric materials have the characteristics of providing both a cushioned ride and also giving greater traction than other materials, however this also has the unfortunate characteristic of having a decreased resistance to sharp objects.

Bicycle tires usually have a narrow outer rubber casing having a thin cross-section and an inner, air filled, butyl material inner tube, and they tend to be inflated to a much higher pressure than is common in motor vehicle tires. Unfortunately sharp objects can easily penetrate the outer rubber casing and puncture the inner tube. Flat tires are a common occurrence for all types of bicycles. Flat tires can be very frustrating for all classes of riders. Children's bikes with pneumatic tires can be especially bothersome. However for the adult performance rider having a flat tire especially in a remote location can be a dangerous experience leaving the rider stranded without any means of transportation. While many bike riders carry tire repair kits, tools and other devices such as air pumps and sealing materials for repairing flat tires, people often have difficulty in making such repairs especially when the need arises. In any event, penetration of the outer tire by thorns or other sharp objects resulting in the puncture of the inner tube and a flat is often a very unpleasant and frustrating experience especially if you are in a relatively remote area.

Various proposals have been made as to how this susceptibility to puncture may be avoided, with varying degrees of success. Methods which attempt to prevent puncture altogether include so-called tire liners which are attached to the inside of the tire casing or sandwiched by air pressure between the casing and an inner tube. In the past such liners have often been expensive and added significantly to the weight of the tire resulting in increased difficulty in propulsion for a cyclist.

Other solutions have sought to use solid rubber tubes in place of the air filled tube. While these do solve the problem of air loss, the high weight and lack of cushioning render the bicycle almost unrideable due to the sluggish nature and hard jarring ride that the bicycle with solid tubes imparts to the rider. Solid tubes are not accepted by any performance cyclist.

It is common to fill tires for off-road vehicles such as farm tractors or road-construction equipment with liquid, most often either water or, in colder climates, a solution of calcium chloride or ethylene glycol or propylene glycol and water. Such liquid acts as ballast for increasing traction and reducing tire wear. Finally, injected liquid solutions with small fibers in suspension have also been employed, however these are short term, heavy and quite messy to install.

Examples of prior art tires and/or tubes are as follows.

U.S. Pat. No. 4,471,827, which issued in 1984 for a “Non-pneumatic insert tube for tires” shows a non-pneumatic insert tube for a tire adapted to be mounted upon a circular rim. The insert tube is an elongated resilient plastic cylinder having a thin wall defining a continuous bore which extends throughout the entire tube length.

U.S. Pat. No. 5,795,414, which issued in 1998 for a “Puncture resistant tire assembly” shows a tire assembly for a pneumatic tire that gives a puncture resistant capability. The tire assembly includes an inner tube with an outer periphery having a plurality of protruding deflectable structures which are circumferentially continuous about the inner tube body.

U.S. Pat. No. 6,418,991, which issued in 2002 for a “Puncture proof inner tube”, provides an improved pneumatic tube formed from a semi-rigid, air-tight rubber core encased by a plurality of thin, armoring Kevlar layers bonded to the exterior wall of the core.

US Published Application No. 2010/0084064, entitled “Puncture free tire tube, puncture free tire, and method for fitting tire tube to tire” shows a puncture free tire tube to be fitted under compressive deformation into a tube housing space of an annular tire outer wall, which is detachably fitted to an annular rim, the puncture free tire tube contains a long member extrusion-molded with an elastomer as a raw material, and has a cross sectional area of from 1 to 1.3 times a cross sectional area of the tube housing space of the tire outer wall and a length corresponding to a circumferential length at a center of the cross section of the tire outer wall.

Polymer foams, as a general class, are made up of a solid and a gas phase mixed together to form a foam. This generally happens by combining the two phases too fast for the systems to respond in a smooth fashion. The resulting foam has a polymer matrix with either air bubbles or air tunnels incorporated in it, which is known as either closed cell or open cell structure. Closed cell foams are generally more rigid while open cell foams are more flexible. The gas that is used in the foams is termed a blowing agent

A trailer vehicle is known from DE 10 2011 007 943 B4, which is constructed for coupling to a towing vehicle. The trailer vehicle has a front and rear axle designed in each case as a steering axle with a steering system having a front axle which executes steering independently and the rear axle is coupled to the front axle. The trailer vehicle includes a loading space between the front and rear axle, wherein a floor plate situated in close proximity to the ground. Furthermore, a portal arch is provided, which transfers tractive forces affecting the front and rear axle together with the floor platform. A disadvantageous associated with this trailer vehicle relates to the significant effort required to urge the inner carriage onto the floor platform.

SUMMARY OF THE INVENTION

In one embodiment, a compliant insert is provided for a wheel assembly including a compliant outer tire and an inner rim, comprising: at least one arcuate segment: (i) filling at least a portion of an internal cavity defined by, and between, the compliant outer tire and inner rim, (ii) defining at least one cross-sectional plane aligned with a radial of the wheel assembly, (iii) having an outer portion circumscribing an inner portion along the at least one cross-sectional plane, and (iv) including interlocking end portions to form a continuous circumferential ring.

According to another embodiment, a method is provided for making a multi-element tire insert. This embodiment includes the steps of: (i) molding at least one arcuate segment defining an inner portion having a first compliant material of a first stiffness value and an outer portion having a second compliant material of a second stiffness value, (ii) bonding the inner portion of the arcuate segment to the outer portion of the arcuate segment, and (iii) interlocking the end portions of the arcuate segment to form a continuous circumferential ring. In this embodiment, the outer portion of the arcuate segment is molded to conform to the internal geometry of a compliant tire.

The present invention replaces any pneumatic inner tube in a wheel-tire assembly, with a multiple layer foam insert that can emulate and imitate the performance and weight of a pneumatic system through the manipulation of the ratios of the cross sections of the multiple foam layers. The insert eliminates problems of loss of air suffered by air filled inner tubes while preserving the performance and weight of the pneumatic tire and tube system that is used for bicycles, motorcycles, automobiles, trucks and other tire/tube pneumatic systems.

The materials of the foam insert contribute to its function, durability and weight. Through the use of modern materials such as extruded multicellular copolymers, the resilience, durability and energy return necessary to establish the feel and ride of a pneumatic tube can be realized. The use of these high energy copolymers in combination with light weight high strength extruded polystyrene in the core of the product can create a platform from which multiple sizes and multiple layer constructions can be made in any combination needed to address all types of uses, pressures and weights. This technique is a novel approach to the replacement of pneumatic structures in many possible areas of transportation.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a sectional view of a tire insert.

FIG. 2 shows a cut-away perspective view of an arcuate length of tire insert, with the outer layer cut away to show the inner layer.

FIG. 3 shows a sectional view of second embodiment of a tire insert.

FIG. 4 shows a sectional view of a third embodiment of a tire insert.

FIG. 5 shows a foam tire insert as mounted on a rim, within a tire.

FIGS. 6A-6F shows a first method of forming a tire insert.

FIGS. 7A-7E show a second method of forming a tire insert.

DETAILED DESCRIPTION OF THE INVENTION

The foam tire insert of the invention can replace pneumatic tubes, especially in bicycles, although the insert can also be used in other applications where air-filled tubes or tires are used today. The insert is made through a foam construction technique using multiple layers of differing foam materials to yield a product that can emulate the feeling and performance of pressurized air in a tire and tube system, without significantly increasing the weight over an average thickness pneumatic tube. With such a construction technique with modern materials the need for pneumatic tubes can be eliminated for large classes of users.

The insert can made as a one piece annular component at its least expensive embodiment. Other embodiments can be arrived at by splitting the insert and mounting a clipping device at each end in order that the foam insert can be mounted without taking the wheel off of the bicycle. In addition, different quality level embodiments can be produced using different materials and different construction methods. This allows for different market segments by price and performance to be individually addressed.

FIGS. 1 and 2 show cross sectional views of a compound (multiple layer) foam tire insert 10 according to one embodiment of the invention, in which the insert 10 is formed of a combination of two distinct types of plastic foams known as polymer foams.

The core 1 of the insert 10 is formed of a stiff, structurally durable, lightweight foam material. The core 1 contributes to providing the long term structural integrity of the insert 10, and also provides the strength and mass that will provide the foundation for the outer layer 2 to rest upon. An appropriate material for the core 1 of the insert 10 would be light weight, non-compressible, flexible material that is in the class of closed cell cross-linked ethylene copolymer foams, closed cell cross-linked polyethylene foam (XLPE) or other commercially available cross linked polyethylene foams. These materials help the insert 10 emulate the structural air pressure that a pneumatic system provides.

The primary characteristics of this structure are light weight, less than 5% compressibility, less than 1% retained deformation under-load and after load relief, long term structural integrity, ease of handling and molding to high tolerances and low cost. The closed air cells in the structure help in emulating and providing the structural component of the system. The desired material characteristics of the material should allow the cell walls to be flexible enough to undergo some level of deformation while showing high retention of structural design after loading.

The outer layer 2 is formed of a different foam material from the material in the core 1, and is responsible for providing to the rider the feel and performance of a pneumatic tube system. The material of the outer layer 2 in this embodiment preferably has significant characteristics of energy return, wide temperature tolerance, shape retention, durability over time and the ability to be extruded in precision tolerances. Preferably, the material of the outer layer 2 has the property that it does not become rigid in a range of temperatures between −20 C and +40 C, and has the durability to last for three or more years.

An appropriate material for the outer layer 2 of the insert 10 would be a class of materials known as styrene-butadiene-styrene, or SBS. This substance is a hard rubber that's used for things like the soles of shoes, tire treads, and other places where durability is important. It's a type of copolymer called a block copolymer. Its backbone chain is made up of three segments: a long chain of polystyrene, a long chain of polybutadiene, and another long section of polystyrene.

SBS is also a type of unusual material called a thermoplastic elastomer (TPE). These are materials that behave like elastomeric rubbers at room temperature, but when heated, can be processed like plastics. Most types of rubber are difficult to process because they are crosslinked. But SBS and other thermoplastic elastomers manage to be rubbery without being crosslinked, making them easy to process into useful shapes.

The use of SBS as a component in the outer layer 2 of the insert 10 strongly assists the invention in emulating the resilience of the pneumatic structure. One specific type of SBS which is useful as an outer layer 2 in this embodiment is Olefin Block Copolymer (OBC), which are polyolefins with alternating blocks of hard (highly rigid) and soft (highly elastomeric) segments. The block structure of OBCs offers an advantaged performance balance of flexibility and heat resistance compared to random polyolefin copolymers. This material also has the distinct advantage of retaining stable performance characteristics over wide ranges of temperatures insuring correct function in a wide range of environmental conditions.

The outer layer 2 in this embodiment is applied evenly around the outside of the core 1 in a uniform thickness 3 which helps determine the performance characteristics of the product. By varying this dimension 3, the emulation by the insert 10 of pressure and performance of a pneumatic tire tube can be determined.

FIGS. 3 and 4 show cross sectional views of another embodiment of the insert 10, in which the ratio of dimensions and location of the core and outer layer is varied to yield different performance characteristics.

FIG. 3 shows an alternative embodiment of the tire insert 30, which might be used to emulate the feeling of a high pressure, high performance tire of lighter weight. In this embodiment, the core 31 is larger relative to the outer layer 32, than the embodiment shown in FIGS. 1 and 2. The core 31 is offset toward the inner circumference 36 of the insert 30 so that the thickness 33 of the outer layer 32 nearest the inner circumference 36 is less than the thickness 34 of the outer layer 32 near the outer circumference 35 of the insert 30. This provides a high ratio of stiff, light core material 31 vs a lower ratio of high density highly flexible material in the outer layer 32.

FIG. 4 shows an alternative embodiment of the tire insert 40, which might be used to emulate a lower air pressure tire, giving the rider more comfort and forgiveness. In this embodiment, the core 41 is smaller relative to the outer layer 42, than the embodiment shown in FIGS. 1 and 2. As in the embodiment of FIG. 3, the core 41 is also offset toward the inner circumference 46 of the insert 40 so that the thickness 43 of the outer layer 42 nearest the inner circumference 46 is less than the thickness 44 of the outer layer 42 near the outer circumference 45 of the insert 40. This provides a lower ratio of stiff, light core material 41 vs a higher ratio of high density highly flexible material in the outer layer 42. This ratio of compounds will give a ride quality.

The ratio, form and material characteristics of these two materials combined into a tubular structure determine the characteristics of the tire insert of the invention. These two materials can be used in many ratios and in many forms in the tubular insert to emulate the desirable characteristics of a pneumatically inflated tube in such a way as to accurately imitate different types and pressures of tire and tube systems at weights that are competitive with pneumatic systems.

In order to emulate (imitate) the required pressures and performance of a pneumatic system in the multi-layer foam insert model three distinct factors must be considered.

The first factor is the diameter of the cavity into which the foam insert must be inserted. This diameter is the equivalent space that is filled by the pneumatically inflated tube. The accurate measurement of this diameter, at the desired inflated pressure is key to insuring the correct fit and function of the multilayer foam insert. Once this diameter is precisely measured and the pressure of the system defined then the design of the foam insert can begin.

The second factor is modeling the foam structure to achieve the desired weight and pressure emulation of the system. Every tire has a recommended pressure rating. The foam insert must be constructed in such a way that it emulates this required pressure. The core material of the foam insert structure is the determining element in achieving this desired pressure. This inner core material must also be formed from a material that has weight of below (at least) 20 Kg per cubic meter of material. This weight parameter insures that the total structural weight will be acceptable to the consumer. This inner lightweight foam core “backbone” is key to the concept of a light weight high performance structure. Additionally, the core material must offer a kPa high enough to emulate the pressure of the inflated tube. The formula to convert kPa to PSI is 1:0.15. One kPa is equivalent to 0.15 PSI.

Table 1, below, illustrates the levels of kPa and their corresponding PSI. Once the defined Psi has been selected then the corresponding material with the correct kPa can be selected.

TABLE 1 kPa PSI 1 0.15 100 14.50 200 29.01 300 43.51 400 58.02 500 72.52 600 87.02 700 101.53

The third factor to achieve the emulation of the required pressures and performance of a pneumatic system are the characteristics (dynamic and kPa) of the outer layer of the foam insert structure. This outer layer is critical to contributing to the foam structure a dynamic and functional aspect. Without this outer layer, the feel and function of the complete wheel system will be “dead” or “numb”. The tire/wheel system will not perform properly and will not give the rider to the correct road surface performance/feedback. The thickness of this outer layer, in proportion, to the light weight inner foam core can be manipulated to achieve the desired final pressure and function of the system. Within the family of SBS (TPE) of thermoplastic elastomers there are many parameters of performance that can be defined. These material parameters can be manipulated in order to achieve the best performance for a given end user's purposes. The variations in thickness of the outer layer in combination with the almost limitless variations in material properties render the predictive modeling of structural performance problematic. In the end, physical prototyping with laboratory performance measurement will be the optimal method for determining the correct materials and ratios of circumferences of said materials to validate the correct structure of the product.

FIG. 5 represents a sectional view of a bicycle wheel in which the foam insert 10 is mounted on a rim 54, within a tire 58. A foam pad 55 is placed around the rim 54 in the cavity 53 of the rim 54 to support the tire insert 10. The tire 58 has a sidewall 59, which is held within the edges 56 of the rim 54 by a bead 57, and has a tread 50 around an outer circumference 52 which is chemically and physically bonded to the tire 58 through the vulcanization process, as is conventional.

The formation of the structure of the insert 10 can occur, for example, in two ways.

The first method, shown in FIG. 6A-6F is through the use of an extrusion process that is well known and highly employed globally to extrude polyethylene foams.

Step 1: FIG. 6A: By the use of a screw extrusion machine 60 with the correct dimension die 61 a in place, the core 81 can be extruded.

Step 2: FIG. 6B: By the use of a screw extrusion machine 60 with the correct dimension die 61 b in place, the outer layer 82 can be extruded.

It should be noted that steps 1 and 2 could be performed in any order, and the lengths of core 81 and outer layer 82 can be made to length as needed, or long lengths can be made in advance in preparation for the succeeding steps described below, within the teachings of the invention.

Step 3: FIG. 6C: The lighter weight, stiff core material 81 is inserted into the denser more flexible outer layer 82, forming the combined insert 80. Optionally, an adhesive 84 can be applied to the outside of the core 81 or the inside of outer layer 82, so as to provide adhesion between the core 81 and outer layer 82. An appropriate adhesive 84 for this process would be, for example, a low temperature spray-able hot melt adhesive that is hand sprayed on the product manually and then assembled into a final structure. An example of a non-toxic adhesive which could be used is Tec Bond 420 sprayable hot melt adhesive from Hotmelt.com. The extruded core 81 and outer layer 82, optionally connected by adhesive 84, will form the structure of the length of insert 80.

Step 4: FIG. 6D: If the insert 80 was formed from long lengths of core 81 and outer layer 82 material, as noted in step 2 above, the combined insert 80 is cut to the length 62 corresponding to the desired circumference of the finished tire insert 65. Alternatively, if the core 81 and outer layer 82 were formed to exact length 62 in steps 1 and 2 before being combined in step 3, this step can be omitted.

Step 5: FIG. 6E: Adhesive 64 is applied to both ends 63 of the insert 80. An appropriate adhesive 64 for this process would be, for example, a tape that is made with acrylic foam which is viscoelastic in nature. This gives the foam energy absorbing and stress relaxing properties which provides these tapes with their unique characteristics. The acrylic chemistry provides outstanding durability performance. These tapes utilize a variety of specific foam, adhesive, color and release liner types to provide each product/family with specific features. These features can include adhesion to specific or a broad range of materials, conformability, high tensile strength, high shear and peel adhesion, resistance to plasticizer migration, and UL746C recognition.

Step 6: FIG. 6F: The ends 63 of the insert 80 are joined, forming a completed tubular tire insert 65 that is ready for use in a tire system.

The second method is uses a co-extrusion process using an extrusion machine 70 with compound die 73, which is less well known to extrude polyethylene foams. This method, shown in FIGS. 7A-7D comprises the following steps:

Step 1: FIG. 7A: Load the material for the core 81 and outer layer 82 into separate feed hoppers 71 and 72 in the extrusion machine 70, such that the two materials enter the extrusion machine 70 at the same time.

Step 2: FIG. 7B: Operate the extrusion machine 70 with the compound die 73 in place, thereby simultaneously extruding the inner core 81 and the outer layer 82 from the compound die 73 as a length of a complete tubular insert 80.

It should be noted that the insert 80 can be made to length as needed, or long lengths can be made in advance in preparation for the succeeding steps described below, within the teachings of the invention.

Step 3: FIG. 7C: If the insert 80 was formed as a long length of material, as noted in step 2 above, the insert 80 is cut to the length 74 corresponding to the desired circumference of the finished tire insert 78. Alternatively, if the insert 80 was formed to exact length 74 in step 2, this step can be omitted.

Step 4: FIG. 7D: Adhesive 76 is applied to both ends 77 of the insert 80. An appropriate adhesive 76 for this process would be, for example, a tape that is made with acrylic foam which is viscoelastic in nature. This gives the foam energy absorbing and stress relaxing properties which provides these tapes with their unique characteristics. The acrylic chemistry provides outstanding durability performance. These tapes utilize a variety of specific foam, adhesive, color and release liner types to provide each product/family with specific features. These features can include adhesion to specific or a broad range of materials, conformability, high tensile strength, high shear and peel adhesion, resistance to plasticizer migration, and UL746C recognition.

Step 5: FIG. 7E: The ends 77 of the insert 80 are joined, forming a completed tubular tire insert 78 that is ready for use in a tire system.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention. 

1. A compliant insert for a wheel assembly including a compliant outer tire and an inner rim, the compliant insert comprising: at least one arcuate segment (i) filling at least a portion of an internal cavity defined by, and between, the compliant outer tire and inner rim, (ii) defining at least one cross-sectional plane aligned with a radial of the wheel assembly, (iii) having an outer portion circumscribing an inner portion along the at least one cross-sectional plane, and (iv) including interlocking end portions to form a continuous circumferential ring.
 2. The compliant insert of claim 1, wherein the outer portion is fabricated from a compliant material to conform with, and support, the internal geometry of the compliant outer tire.
 3. The compliant insert of claim 1, wherein the inner portion is fabricated from a first compliant material and the outer portion is fabricated from a second compliant material, the first compliant material having a different stiffness than the inner compliant material.
 4. The compliant insert of claim 1, further comprising multiple arcuate segments having interlocking ends wherein a first end of one arcuate segment interlocks with a second end of another arcuate segment.
 5. The compliant insert of claim 1, wherein the cavity defines a three-hundred and sixty degree (360°) circumferential arc and, furthermore, comprising at least two (2) arcuate segments which may be combined to fill the internal cavity.
 6. The compliant insert of claim 1, wherein the cavity defines a three-hundred and sixty degree (360°) circumferential arc and further comprising at least three (3) one-hundred and twenty degree (120°) arcuate segments.
 7. The compliant insert of claim 1, wherein the cavity defines a three-hundred and sixty degree (360°) circumferential arc and further comprising at least four (4) ninety degree (90°) arcuate segments.
 8. The compliant insert of claim 1, further comprising an adhesive for bonding outer portion of the arcuate segment to the inner portion of the arcuate segment.
 9. The compliant insert of claim 2, wherein the inner portion of the arcuate segment is eccentric relative to the outer portion of the arcuate segment, such that the thickness between the outer portion of the arcuate segment and the internal geometry of the compliant outer tire is less than the thickness between the inner portion of the arcuate segment and an internal surface of the inner rim.
 10. The compliant insert of claim 3, wherein the first compliant material defines a first stiffness value and the second compliant material defines a second stiffness value and wherein the first stiffness value is greater than the second stiffness value.
 11. The compliant insert of claim 3, wherein the first compliant material of the inner portion of the arcuate segment is a closed-cell foam material.
 12. The compliant insert of claim 3, wherein the first compliant material of the inner portion of the arcuate segment is a cross-linked ethylene copolymer foam material.
 13. The compliant insert of claim 3, wherein the first compliant material of the inner portion of the arcuate segment is a cross-linked polyethylene foam material.
 14. The compliant insert of claim 3, wherein the second compliant material of the outer portion of the arcuate segment is a thermoplastic elastomer.
 15. The compliant insert of claim 3, wherein the second compliant material of the outer portion of the arcuate segment is a styrene-butadiene-styrene block copolymer.
 16. A method of making a multi-element tire insert comprising the steps of: molding at least one arcuate segment defining an inner portion having a first compliant material of a first stiffness value and an outer portion having a second compliant material of a second stiffness value, the outer portion conforming to the internal geometry of a compliant tire; bonding the inner portion of the arcuate segment to the outer portion of the arcuate segment, interlocking the end portions of the arcuate segment to form a continuous circumferential ring.
 17. The method of claim 16, further comprising the step of applying adhesive to the end portions of the at least one arcuate segment to join the interlocking end portions thereof.
 18. The method of claim 16, further comprising the step of forming at least two (2) arcuate segments which, in combination, define an arcuate length of three-hundred and sixty degrees (360°.)
 19. The method of claim 16, further comprising the step of forming three (3) arcuate segments each having an arcuate length of one-hundred and twenty degrees (120°) which, in combination, are joined to form a continuous circumferential ring.
 20. The method of claim 16, further comprising the step of forming four (4) arcuate segments each having an arcuate length of ninety degrees (90°) which, in combination, are joined to form a continuous circumferential ring. 